Sestak led McGinty, who finished fourth in a gubernatorial primary in 2014, by double-digits at the beginning of the month. The establishment rode to the rescue, with EMILY's List, SEIU and the DSCC — making a rare seven-figure expenditure on a party primary — all spending heavily to boost McGinty ahead.

President Barack Obama and Vice President Joe Biden both endorsed McGinty over Sestak, who had a cold relationship with party leaders. McGinty featured Obama's endorsement constantly in advertising, and Biden campaigned with her twice. Some Democrats questioned the heavy spending, noting there was little evidence McGinty stood a better chance in the general than Sestak.

In her victory speech, McGinty immediately shifted to the coming campaign against GOP Sen. Pat Toomey, referring repeatedly to the "Trump-Toomey ticket."

"With all we have to fight for, and with the White House, the Senate and the U.S. Supreme Court at stake, we can’t afford to sit back," McGinty said. "Not when the Toomey-Trump team is so eager to promote a brand of bigotry and hatred and eager to reverse the progress made under President Obama."

Toomey has consistently led McGinty in polling, with a significant advantage in name identification. Toomey also has $9.1 million on hand as of early April. McGinty's campaign account is likely empty following the contested primary. The Toomey campaign immediately sprung on McGinty's weaknesses.

“Democrats have thrown in their lot with a far left machine politician who has an ethics rap sheet a mile long,” Toomey spokesman Ted Kwong said. “Katie McGinty supports every item on her party bosses’ liberal agenda, and is Pennsylvania’s number one abuser of the revolving door between government and corporate boards. McGinty makes government work for her, not for us, and that’s not what our state is looking for in a U.S. Senator.”

Van Hollen also surged late in Maryland, where the expensive and heated primary split along racial lines. Exit polls show Van Hollen won white voters by 52 percentage points, while Edwards carried African-Americans by 32 points. Edwards attacked him as a deal-making sellout to progressives in the House, but a super PAC backing her overstepped the attack, using footage of Obama in an ad — and drawing a sharp rebuke from the White House and Democratic leaders in Congress.

Van Hollen, the son of diplomats, has been a Democratic rising star for years and was a close ally of the party’s leadership in the House. Edwards emphasized her biography and identity in television advertising and interviews with progressive media, noting she put herself through law school and was a single mother, a message she believed would appeal to an electorate that was 46 percent black, according to exit polls.

In her concession speech, Edwards warned that the Democratic Party was failing to adequately diversify its ranks.

"Maryland is in the verge of having an all male delegation in a so-called progressive state," Edwards said, lamenting the lack of black women in the Senate.

“Putting people against each other based on religion, ethnicity, or based on race, that is not who we are in the United States," he said.

The Senate results are a split for EMILY's List. The group spent nearly $3 million backing Edwards, hoping to keep retiring Sen. Barbara Mikulski’s seat held by a female Democrat. Their heavy spending drew skepticism from other Democrats, who believed the money would be better spent against Republicans in the fall.

"Races like [Edwards'] are exactly why EMILY’s List exists: to even the playing field and give women a fighting chance," EMILY's List President Stephanie Schriock said. "We know that isn’t always comfortable for some in the progressive movement, but if electing an African-American woman to the Senate was easy, we’d have done it more than once in our nation’s 240-year history."

But the Democratic women’s group also played a crucial role boosting McGinty into the general election against Toomey, a critical battleground race that could decide the Senate majority this fall.